Conventionally, intruding object detection apparatuses using a millimeter wave radar have been proposed for the purpose of detecting an intruding object in a region such as the interior of the crossing of a railroad.
For example, in Patent Literature (hereinafter, abbreviated as PTL) 1, an antenna and a reflective reference point of a radar are placed in a predetermined position of the region for detection, and a detection processing section determines existence of an intruding object on the basis of the relationship between a reflected wave (measurement reflected wave) measured and a reflected wave from the reflective reference point.
Moreover, in PTL 1, two or more reflective reference points and antennas are placed so as to eliminate any region in which an intruding object cannot be detected (non-detected region) in a region for detection, such as a crossing, and the intruding object is detected over the whole region for detection by suitably switching the antenna which receives a signal inputted into the detection processing section.